1. Field of the Invention
This invention relates to a mechanism for mounting and dismounting, with respect to an apparatus body, a frame member supporting a screen-like photosensitive medium having a number of fine openings (hereinafter referred to as the screen).
2. Description of the Prior Art
The screen described herein is known from our U.S. Pat. No. 4,143,965 and U.S. Pat. No. 3,680,954. In an apparatus for forming an image by the use of such screen, it has been practised to form the screen into the shape of a drum as disclosed in U.S. Pat. No. 3,985,432. As an example of the means for forming the screen into the shape of a drum, use may be made of a partly cut-away cylindrical frame member 2 as shown in FIG. 1 in the accompanying drawings and the screen 1 may be stretched along the cut-away portion of the frame member 2 and adhesively secured thereto. In FIG. 1, reference character 3 designates cylindrical portions and reference character 4 designates a connection portion. Alternatively, such frame member may be constructed by joining the connecting portion 4 to the cylindrical portions 3. It is very difficult for the frame member 2 to maintain sufficient rigidity because of the limited positional relation between the frame member and a corona discharger disposed therewithin. Also, the screen itself is a net-like member comprising a plurality of very thin layers of several microns to several tens of microns and is structurally weak against extraneous forces.
On the other hand, constituent members such as primary latent image forming means and latent image stabilizing means are disposed around and in proximity to the drum-shaped frame member supporting the screen (hereinafter referred to as the screen drum). Therefore, if a great extraneous force is exerted on the screen drum during the mounting or dismounting thereof with respect to the apparatus body, the frame member may be deformed to thereby twist and damage the screen or deform the configuration of the openings thereof. Also, during the mounting or dismounting, the screen is moved along the rotary center shaft thereof and in that case, there is a danger that the screen is brought into contact with the constituent members around the screen drum, whereby the screen is damaged. Further, it is necessary to dispose a corona discharger within the screen drum and this unavoidably complicates the construction for permitting the internal discharger to be disposed during the mounting or dismounting of the drum.